Biogenic sulfur emissions and aerosols over the tropical South Atlantic: 1. Dimethylsulfide in sea water and in the atmospheric boundary layer

Abstract

We measured dimethylsulfide (DMS) in air (DMSa) and surface seawater (DMSw) on board the R/V Meteor during February–March 1991 on the tropical South Atlantic. Samples for the determination of DMSa were taken through a fluorinated ethylene/propylene Teflon inlet ≈33 m above sea level, preconcentrated by adsorption onto gold wool in quartz tubes, and analyzed by gas chromotography with flame photometric detection. The DMSa instrument is fully automated, providing improved precision, and processes up to four samples per hour. Over most of the cruise track, which followed the 19°S parallel between Brazil and Africa, DMSw, was significantly correlated to climatologically averaged chlorophyll concentrations obtained from coastal zone color scanner data, suggesting that remote sensing may be useful for estimating seawater DMS levels at least in some ocean regions. The cruise track proceeded from waters of low roductivity (off the coast of Brazil and in the subtropical gyre) to higher productivity (the Benguela Current and the upwelling region off Namibia and Angola); meteorological conditions were steady with consistent easterly winds. DMS values for air and water were low (≈ 50 ppt and 1–2 nmol L−1, respectively) in the areas of low productivity and increased simultaneously (≈ 100–300 ppt and 3–15 nmol L−1) as productivity increased. DMS sea‐to‐air fluxes (average 7.3 μmol m−2 d−1) were calculated based on different parameterizations; for the study region the differences between the results obtained from the different models were minor. DMSa was strongly correlated to its emission flux from the sea surface as estimated from DMSw and meteorological parameters. This suggests that the air/sea transfer parameterizations used are suitable for providing estimates of DMS flux from the oceans.